Evidence of icy grains in the coma of comet 103P/Hartley 2 from ground based observations G. P. Tozzi 1, P. Patriarchi 1, E. Mazzotta-Epifani 2, L. M. Lara 3, O. Hainaut 4, H., Boehnhardt 5, J. R. Brucato 1, Del Bó 6, J. Licandro 7, K. Meech 8, P. Tanga 6 1 INAF-Osservatorio Astrofisico di Arcetri, Firenze (I), 2 INAF-Osservatorio Astronomico di Capodimonte, Napoli (I), 3 Instituto de Astrofísica de Andalucía - CSIC, Granada (E), 4 ESO, Garching (D), 5 Max Planck Institute for Solar System Research, Katlenburg-Lindau (D), 6 Observatoire de la Cote d'Azur, Nice (F), 7 Instituto de Astrofisica de Canarias, Tenerife (E), 8 Univ. Hawaii, Institute for Astronomy, Honolulu (USA)

Good News!!!! We discovered water in a comet!!! Bad News!!! We are more than 30 years in delay!!! It is an indirect evidence of water in a comet!

EPOXI Observations

ESO Observations The NTT observations started on October 31 and ended on the morning of the November 6. Rh=1.06 AU; Δ= AU; α= o ; Pat= o The main goal of the observations was the characterization of the coma solid component ans search for organic grains. Most of the observations were images of the comet in the visible, using two cometary filters centered in regions free of gas emission, in the blue and in the red (Bc filter: λ = 4430 Å and FWHM = 33 Å; Rc filter: λ = 6840 Å and FWHM = 74 Å). Observations in the near-IR were also performed one night, to check the color of the solid component in the 0.44 to 2.16 μm range. After the usual data reduction, all the images were calibated in Af, i.e. the Albedo (A) multiplied by the filling factor (f).

Example

Analysis With the Σaf function, the activity of the comet has been checked and the images (in Bc and Rc) with the minimum activity have been identified

The Afρ measured at 4000 km on the images at minimum activity is 78 and 93 cm in Bc and Rc, respectively This imply a reddening of the normal dust of 7 %/1000 Å The images corresponding to the minimum activity have been subtracted from all the other, to get a map of the solid component released during the “outbursts” Note that the comet rotate with P=18.8 h, at the time of the observations

Maps for Bc, in function of the day and phase

Maps for Rc, in function of the day and phase

It seems that the “outbursts” are emitted at different phases in two preferred directions: at PA=80 and PA=140 deg To study those outburst, the images have been integrated in polar coordinates around PA=80 and 140 deg, over about 80 deg. The resulting profiles vs ρ could be fitted with a function of the kind ΣAf(ρ) = ΣAf 0 + ΣAf 1 e -{ ρ/L}

The product (ΣAf 1 * L) is equal to the cross section (SA) of the solid component released is such a direction. The variation of L (during the same nitgh) can give the projected velocity of expanding of the outburst. It results of the order of m/s, by analyzing the outburst of the same night, that of Nov. 6 at PA=80 This imply that during 24 h the outburst moves at maximum 1500 km, well inside the field of view of the observations. So the solid component released during an outburst should be seen also the night after. But this is not the case.

SA in Bc and Rc in funtion of the phase To match the SA in Bc in respect to the Rc, the previous have been multiplied by 1.4. That means that the Albedo in Rc is 40% more than that in Bc. This correspond to a reddening of 17%/1000Å, quite different from that of the normal coma. The SA decreases by a factor 2 with a phase difference of ~ 100 deg, corresponding to about 5 hours!

Conclusion The solid component released during the outbursts is very different from the dust of the normal coma The grains released by the outburts move with a very low projected distance. So they should remain in the FOV during some rotation phases. The cross section of those grains however decreases a lot in short time. So they should sublimate. Probably we observed the ICY GRAINS (Snow Storm) observed from the spacecraft!

More soon!